ANTIECDYSTEROID EFFECTS OF BRASSINOSTEROIDS IN INSECTS

Brassinosteroids show striking structural similarities with ecdysteroids, the moulting hormones of insects and other arthropods. When ingested by insects with their food, brassinosteroids are resorbed and were found to affect insect development. In cockroaches the duration of a larval stage was increased. The effect was dependent on the dose and type of brassinosteroid applied. In ecdysteroid bioassays with Dipteran tissues, brassinosteroids exhibited a significant antagonistic activity. This effect was dose-dependent and reversible. Brassinosteroids were also found to have an influence on the electrical activity of insect neurons. When tested in a radioreceptor assay, brassinosteroids showed affinity for the ecdysteroid binding site of the ecdysteroid receptor. These observations indicate that brassinosteroids interfere with the hormone system of ecdysteroids directly at the site of their action. Brassinosteroids may have both ecdysteroid agonistic and antagonistic activities. They represent the first true antiecdysteroids observed. Due to the fact that they are natural products, brassinosteroids are potential candidates for a safer insect pest control.